Injury to the anterior cruciate ligament (ACL) results in a threat to an active lifestyle and exposes the patient to risk of early osteoarthritis. ACL reconstruction is typically chosen by individuals to allow a return to their previous work and sports activities. The results of primary ACL reconstruction have in general been good at restoring functional stability, but patients' long-term outcome remains unknown. The Multicenter Orthopaedic Outcomes Network (MOON) is an established consortium designed to enroll and longitudinally follow a population cohort of ACL reconstructed patients to determine the modifiable predictors (or risk factors) of long-term outcomes of ACL reconstruction in order to establish patient-specific predictive models of clinically important outcomes. The objective of this prospective multicenter cohort of ACL reconstructions is to identify both the long-term prognosis and the potentially modifiable predictors of sports function, activity and general health through validated patient-reported outcomes, symptoms and signs of osteoarthritis (OA), and incidence of ACL reconstruction graft and/or contralateral ACL failures. During the past funding cycle we have enrolled over 2,000 patients and have completed two year follow-up on 85% (1989/2340) of our cohort using validated patient-reported outcome questionnaires and 93% (2176/2340) via phone follow-up. In addition, a nested cohort of 125 ACL reconstructed patients returned onsite after 2 years for a comprehensive clinical assessment, radiologic measurements, along with completing their patient-reported assessment. The objective of this competitive renewal is to longitudinally follow this captured cohort at six years utilizing the same validated outcome measurements as well as following incidence of clinical graft and/or contralateral ACL failure. Further, we plan to expand enrollment in the onsite nested cohort to determine the predictors of and the correlates from clinical assessment with both the symptoms and signs of OA and validated outcomes (in terms of sports function, activity, and general health). This grant focuses on the predictors for ACL reconstruction outcome at six-year follow-up. This will be accomplished by three Specific Aims. Aim 1 will identify the independent predictors of return to sports function, physical activity level, and patient-reported quality of life. Aim 2 will identify those independent modifiable predictors measured at the time of the ACL reconstruction associated with symptoms of early osteoarthritis at 6 years post-surgery. Aim 3 will identify incidence of additional surgery performed on patients following ACL reconstruction. Once the predictors for good or bad outcomes are identified, surgeons can be educated in potential modifiable variables to improve the outcome.